In general, a battery pack functions to supply a power source of a portable terminal block, and is composed of a battery cell for storing electricity; and a charging circuit for charging and supplying the electricity.
As a charger for charging electricity in a battery pack for this portable terminal block, there is a terminal supply system in which electricity is received from a conventional power source and a power source is supplied to a battery pack via a power supply terminal. However, where the battery pack is attached/detached to/from the charger when a power source is supplied to this terminal supply system, an instant discharge phenomenon occurs due to the different potential difference of terminals disposed in both sides of the battery pack. Therefore, the battery pack has an increasing possibility to start fires as foreign substances are accumulated in the terminals. Also, the life span and performances of the charger and the battery pack may be deteriorated, for example spontaneous discharging in the presence of moisture.
In order to solve these problems regarding the terminal supply system, there has been developed a wireless charger. That is to say, this wireless charger is charged by a secondary coil inside the battery pack when a portable terminal block having a battery pack mounted inside is disposed upwardly in a primary coil of wireless charger. That is to say, electricity induced from an induced electromotive force is charged in the secondary coil by means of the magnetic field generated in the primary coil.
However, these conventional wireless chargers have no practical use since it is possible only to supply a power to a portable terminal block, but they have difficulty in use for other applications.
In particular, the conventional wireless chargers have problems that it is impossible to determine a charging level since they have no additional indicator, and it is also difficult to determine a state of the wireless chargers since a user does not discriminate a respective state in the charging level.
Furthermore, the wireless charger may be damaged due to the increased loss of power in the primary coil when metals are disposed adjacent to the magnetic field generated in the primary coil.